The invention includes embodiments that relate to an improved hollow fiber membrane and to methods of forming the same.
Hollow fiber membranes are advantageously used for liquid and gas separations. For effective separations (e.g., gas separations), membrane selective layers should be nearly defect-free and should be thin (optimally, for example, having a thickness of less than 1 μm) to enable high permeances or flux. Polymeric membranes can be created by making a composite membrane with the selective polymer layer coated on to a support substrate.
Hollow fiber supports can provide the optimum geometry for high production rates and ease of module formation while providing high surface area and membrane packing density compared to flat sheets. Composite hollow fiber membranes can be manufactured by casting the selective layer on a pre-existing porous support. However, it is difficult to form ultra-thin (e.g., ˜0.1 μm), defect-free selective coatings on porous supports. Typically, forming, e.g., a 100 nm defect-free film is a processing challenge. When a film is dried it has minor pin hole defects (<10 nm). For gas separation applications (which have typical size <1 nm or <10 Å), even a small crack in a 100 nm layer can make it defective. The porosity in the support layer also causes the coating to infiltrate and cause uneven coating. Typically, a 1-5 μm coating can be obtained, but below that is a challenge. Endeavoring to make very thin coating leads to spots on the support which remain uncoated (non-uniform coating), and endeavoring to cover all the spots leads to thick coatings.
Thus, a need exists for improved membranes that have, or are conducive to obtaining, a thin and/or near defect-free selective layer on the support.
While certain aspects of conventional technologies have been discussed to facilitate disclosure of the invention, Applicants in no way disclaim these technical aspects, and it is contemplated that the claimed invention may encompass one or more of the conventional technical aspects discussed herein.
In this specification, where a document, act or item of knowledge is referred to or discussed, this reference or discussion is not an admission that the document, act or item of knowledge or any combination thereof was, at the priority date, publicly available, known to the public, part of common general knowledge, or otherwise constitutes prior art under the applicable statutory provisions; or is known to be relevant to an attempt to solve any problem with which this specification is concerned.